Tool for cutting jacket insulation having a retractable knife mounted on a rotatable outer housing



p 1968 J. E. SLONKSNES 3,375,579

TOOIJ FOR CUTTING JACKET INSULATION HAVING A RETRACTABLE KNIFE MOUNTED ON A ROTATABLE OUTER HOUSING Filed June 8, 1967 INVENTOR 8 JOHN E. SLONKSNES Y m .M QQQ fig w Q QM ATTORNEYS. v.

United States Patent 3,375,579 TOOL FOR CUTTING JACKET INSULATION HAV- ING A RETRACTABLE KNIFE MOUNTED ON A ROTATABLE OUTER HOUSING John E. Slonksnes, Sayreville, N.J., assignor to General Cable Corporation, New York, N.Y., a corporation of New Jersey Filed June 8, 1967, Ser. No. 644,678 9 Claims. (Cl. 3090.8)

ABSTRACT OF THE DISCLOSURE This specification discloses a tool for cutting through the jacket insulation of an electric cable so that the jacket can be conveniently stripped from the cable. The tool has a knife blade in a holder, and there is an opening in the holder through which the cable passes. The blade can be retracted to permit the cable to be inserted through the opening, and the blade is then moved into a working position where it cuts into the insulation to a controlled depth as the tool is pulled along the length of the cable, or as the cable is pulled through the opening. The blade holder is carried by and is rotatable in an outer housing so that the knife can out along a spiral course when used on cables having conductors twisted together and covered by a common insulation jacket. An eccentric adjusts the blade for the desired depth of cut.

Brief description of the invention This invention is a device that provides a quick and easy way for stripping outer jackets from electrical cables, particularly those having non-round cross sections that remain relatively constant in size. A common construction illustrating this type of cable consists of two in dividually insulated round conductors that are twisted together with a uniform lay and around which is extruded a close-fitting retaining jacket of elastometric-type material, such as polyethylene or polyvinyl.

When it is required to strip the outer jacket from this type of cable, the toughness of the jacket material and the warped surface generated by the lay of the twisted conductors makes it difiicult to use conventional stripping tools. For example, if a knife is used to slit open the jacket in an axial direction along the warped surface, the operation is slow and hazardous. Aside from the possibility of personal injury, the inner members of the electrical cable may be damaged by a slip of the knife.

This invention provides a stripping tool which is placed on the cable by sliding the tool over the end of the cable up to whatever length is to be stripped. A pivotted slitting knife blade, mounted in the tool, is then shifted into cutting position and the assembly is pulled in an axial direction opposite to the direction in which the tool was installed. This operation cuts through the outer jacket along a line traversed by one extremity of the minor axis of the cable cross section. The jacket can then be easily opened and pulled away from the conductors. By proper adjustment of the cutting knife, no damage is caused to any of the inner components of the cable.

A circumferential cut through the jacket is preferably made prior to the insertion of the cable into the tool assembly and is made at the location where the stripping is to begin. The circumferential cut is made with a cutter shaped to the cross section of the jacket.

In the preferred construction, a die holder is used as an outer housing of the stripping tool assembly and the part of the assembly which carries the knife is supported in the die holder by anti-friction bearings which permit the knife blade and its supporting means to rotate in the die 3,375,579 Patented Apr. 2, 1968 holder during the relative movement of the knife and cable,

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

Brief description of the drawing In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIGURE 1 is a fragmentary view showing the stripping tool assembly of this invention with a die holder used as the outer housing and with portions of the die holder handles broken away;

FIGURE 2 is an enlarged rearward view of the knife blade holder of FIGURE 1; and FIGURE 2 is partly in section with the section taken along the line 2-2 of FIGURE 3; and

FIGURE 3 is a greatly enlarged sectional view taken on the line 33 of FIGURE 1.

Detailed description of the invention The stripping tool assembly shown in the drawing includes a conventional die holder 10 having a hub portion 12 with handles 14 projecting from opposite sides of the hub portion. There is a knife blade holder 16 located in an opening 18 which extends through the hub portion 12, and this knife blade holder is rotatable on the hub portion 12 on ani-friction bearings, as will be explained in connection with FIGURE 3.

There is an opening 22 through the blade holder 16; and this opening 22 is of substantially the same shape as the cable with which the stripping tool is to be used. When the tool is to be used on larger or smaller cables, the blade holder 16 can be removed and replaced by another blade holder having an opening of the correct size for the different cable.

A knife blade 24 is carried by the holder 16. This knife blade 24 is movable from a retracted position, in which it does not extend into the opening 22, into a working position in which it does extend into the opening 22 far enough to cut through the jacket of a cable which is inserted into the opening 22.

The blade 24 is shown in full lines in its working position in FIGURES 1-3; and it is also shown in dotted lines in its retracted position in FIGURE 3.

The blade 24 is supported on a stud 28 which serves blade 24 up and down with respect to a line 36 which is the axis of the opening 22. Thus the blade 24 is adjustable to change the depth of cut in accordance with the wall thickness of the jacket on the cable.

The shaft 30 rotates in the bore 32 as a bearing and has a slot 38 in its outer end so that the shaft can be rotated with a screw driver. In order to hold the shaft 30 in any desired adjusted position, there is a set screw 40 in a threaded opening which extends through the'blade holder 16 and into the bore 32 at right angles to the axis of the bore 32. In the illustrated construction, the shaft 30 is of reduced diameter intermediate its ends and at the portion of the shaft 30 with which the set screw 40 comes in contact.

The knife blade 24 is held in a slot 44 in the blade holder 16. The stud 28 extends across this slot 44 and contacts with a screw 46 on the other side of the slot. The screw 46 fits into a threaded portion of the bore 32 and provides a stop for determining the extent to which the shaft 30 can be inserted into the bore 32 when the apparatus is assembled. I

The relative movement of the cable with respect to the knife blade 24 is toward the right in FIGURE 3 and the knife blade is, therefore, made with a cutting edge 50 which extends upward along the lefthand side of the knife blade for a distance equal to the deepest cut for which the knife blade is intended to be used.

A set screw 54 threads into an opening which is located partly in each of the faces of the blade holder 16 on opposite sides of the slot 44. This set screw provides an adjustable stop with which the knife blade 24 comes in contact when moved into working position. A lock nut 56 holds the set screw 54 in any adjusted position.

FIGURE 2 shows the way in which the blade 24 makes a cut 60 through a jacket 62 of a cable 64 as the cable moves past the knife blade 24. This cable 62 has two round conductors 66, each of which is covered with electrical insulation 67 and these insulated conductors are twisted together with a uniform lay to provide a cable of substantially oval cross section substantially the same as the shape of the opening 22. The side of the opening 22 opposite the knife blade 24 provides a backing against which the knife presses the cable 64 in order to hold the cable in position with respect to the knife during the cutting operation.

FIGURE 3 shows the hub portion 12 in section. The opening through this hub portion has a raceway 70 for receiving anti-friction bearings, such as roller bearings 72.

The knife holder 16 has a hub 74 with a peripheral raceway 76 for contact with the antifriction bearings 72. The raceway 70 is recessed so as to prevent axial displacement of the anti-friction bearings 72, and the hub 24 has a shoulder 78 at its right-hand side for preventing displacement of the blade holder 16 toward the left in FIG- URE 3.

At the end of the hub 26 which is remote from the knife blade, the hub 76 must be of small enough diameter for insertion into the circle of bearings 76 when the apparatus is originally assembled. The parts are then held in assembled relation by means of a ring 80 which is attached to the left-hand end ofthe hub 74 by screws 82. This ring 80 extends radially beyond the inner limits of the bearings 72 and provides a shoulder for the left-hand side of the raceway 76. It will be understood that the antifriction bearing construction can be reversed with the removable raceway shoulder on the outer raceway 70 instead of the inner raceway 76, as shown. However, the illustrated construction has the advantage of permitting use of a conventional die holder for the hub portion 12 of the stripping tool of this invention.

The advantage of using a die holder is that they have the handles 14 (FIGURE 1) as gripping surfaces by which the tool assembly can be movedwith considerable force for cutting the jacket of large-size cables. Also, die holders are a standardized product which is available commercially so that only the knife blade holder 16 of this invention need be provided as a special item for the assembly.

The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as described in the claims.

What is claimed is:

1. An insulation jacket stripping tool including, in combination, a knife blade holder with an opening through which passes a noncircular insulated cable having a helical lay, a grip portion on the tool for obtaining relative movement of the blade holder and the cable lengthwise of the cable, the grip portion having bearings in which the knife blade holder is rotatable in said grip portion about the axis of the opening, said opening being unsymmetrical about said axis and having contacting portions to prevent rotation of the cable in the opening whereby the knife blade holder rotates with the helical lay of the cable, a blade carried by the holder and movable with respect to the holder between a retracted position that leaves the opening through the holder unobstructed and a working position in which the blade projects into the opening for contact with the insulation of the cable that passes through the opening, the blade when in working position being oriented to cut the insulation along a line extending lengthwise of the direction of relative movement of the holder and the cable, and means for moving the blade selectively between its retracted and working positions.

2. The stripping tool described in claim 1 characterized by the blade holder having a radially extending slot therein into which the blade extends and into which the cutter end of the blade moves when the blade is shifted into retracted position, said slot being in a plane with the axis of said opening in the holder.

3. The stripping tool described in claim 1 characterized by adjustable means for changing the extent to which the blade projects into the opening through the holder when the blade is in working position to control the depth of cut of the blade into the insulation.

4. The stripping tool described in claim 3 characterized by the opening through the blade holder having a space shaped to fit the cable and against which the cable is held by the blade when the blade is in working position.

5. A tool as described in claim 1 for stripping insulation from a non-circular cable having two individually insulated round conductors twisted together, with uniform lay and covered with a close fitting retaining jacket, and characterized by the opening through said holder being of the same shape as the transverse cross section of the cable.

6. The stripping tool described in claim 1 characterized by anti-friction hearings in the grip portion of the tool and in which the blade holder rotates to obtain the relative rotation of the holderwith respect to the cable.

7. The stripping tool described in claim 6 characterized by the grip portion of the tool being an outer housing having an opening through which the blade holder extends, said opening having a raceway spaced from the blade holder, the blade holder having a hub portion which is located in the opening through the outer housing and which has a raceway aroundits circumference, anti-friction hearings in the space betweenthe raceway of the outer housing and the raceway on the hub of the blade holder, and a retainer for the anti-friction bearings located at the end of the housing opening remote from the knife blade.

8. An insulation jacket stripping tool including, in combination, a knife blade holder withan opening through which an insulated cable passes, a blade carried by the holder and movable withrespect to the holder between a retracted position that leaves the opening through the holder unobstructed and a working position in which the blade projects into the opening for contact with the insulation of the cable that passes through the opening, the blade when in working position being oriented to cut the insulation along a line extending lengthwise of the direction of relative movement of the holder and the cable, means for moving the blade selectively between its retracted and working positions and a grip portion on ,the tool for obtaining relative movement of the blade holder and the cable lengthwise of the cable, characterized by the blade holder having a radially extending slot therein into which the blade extends and into which the cutting end of the blade moves when the blade is shifted into retracted position, a pivot support extending acrossthe slot and through the blade, bearing means for the pivot support eccentric of the portion of be support on which the blade moves when shifted from Workingto retracted position, means for rotating the eccentric portions of the support to raise and lower the blade with respect to the opening through the holder to change the distance which the blade extends into the opening for controlling the depth of cut of the blade, an adjustable stop with which the blade contacts when moved into working position, said adjustable means comprising a set screw threaded into a portion of the holder, and another set screw for locking the eccentric bearings in adjusted position.

9. The stripping tool described in claim 8 characterized by the outer housing having a center hub portion with an opening having a bearing raceway therein, the blade holder having a hub portion beyond the knife with an outside surface providing a complementary bearing raceway, antifriction hearings in the space between the raceways and at angularly spaced locations around the blade holder, a bear- 10 ing retainer attached to the hub of the blade holder at the end of the hub remote from the knife blade, and the grip portion of the tool comprising handles extending radially from opposite sides of the outer housing.

References Cited UNITED STATES PATENTS 1,165,176 12/1915 Horner 30-90.6 2,391,721 12/1945 Lundeen 819.51 X 2,419,511 4/1947 Vaughan 819.5 X 2,561,099 7/1951 COSteIOW 30-91.] 2,624,221 1/1953 Schneider 819.51 2,761,211 9/1956 Grant 3090.8

MILTON S. MEHR, Primary Examiner. 

